The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Plasma etching is frequently used in semiconductor fabrication. In plasma etching, ions are accelerated by an electric field to etch exposed surfaces on a substrate. The electric field is generated based on RF power signals generated by one or more radio frequency (RF) generators of a RF power system. The RF power signals generated by the RF generators must be precisely controlled to effectively execute plasma etching.
A RF power system may include a RF generator, a matching network, and a load, such as a plasma chamber. The RF power signals may be used to drive the load to fabricate various components such as integrated circuits, solar panels, compact disks (CDs), digital versatile (or video) discs (DVDs), and the like. The load may include any of a number of elements or devices driven by a RF signal, including, by way of a non-limiting example, a plasma chamber. The load may include broadband mismatched loads (i.e. cables with mismatched resistor terminations), narrowband mismatched loads (i.e. a 2-element matching network) and resonator loads.
The RF power signals are received at the matching network. The matching network matches an input impedance of the matching network to a characteristic impedance of a transmission line between the RF generator and the matching network. This impedance matching aids in minimizing an amount of power applied to the matching network in a forward direction toward the plasma chamber (“forward power”) and reflected back from the matching network to the RF generator (“reverse power”). Impedance matching also assists in maximizing forward power output from the matching network to the plasma chamber.
In the RF power supply field, there are typically two approaches to applying the RF signal to the load. A first, more traditional approach is to apply a continuous wave signal to the load. The continuous wave signal is typically a sinusoidal wave that is output continuously by the power supply to the load. In the continuous wave approach, the RF signal assumes a sinusoidal output, and the amplitude and/or frequency of the sinusoidal wave can be varied in order to vary the output power applied to the load. A second approach to applying the RF signal to the load involves pulsing the RF signal, rather than applying a continuous wave signal to the load.